1. Field of the Invention
This invention relates to an apparatus, method and system for defining a pattern on a substrate and more particularly relates to an apparatus, method and system for fabricating a patterned media imprint master having increased data track density.
2. Description of the Related Art
Nearly every computer in use today uses one or more hard disk drives to store changing digital information in a relatively permanent form. Hard disk drives are also becoming increasingly pervasive in media players, digital recorders, and other personal devices.
Hard disks typically comprise high precision aluminum or glass disks coated on both sides with a special thin film media designed to store information in the form of magnetic patterns. The disks are rotated at high speeds, and electromagnetic read/write heads are used to either record information onto the thin film media, or read information from it.
Thin film media employed in hard disk drives typically comprise a thin, continuous layer of magnetic grains that may be magnetized in a particular orientation by a strong magnetic field. A read/write head, for example, can record information by creating a local magnetic field that orients a cluster of grains, known as a bit, in one direction or the other. To increase the capacity of disk drives, manufacturers are continually striving to reduce the size of bits and the grains that comprise the bits.
The ability of individual magnetic grains to be magnetized in one direction or the other, however, poses problems where grains are extremely small. The superparamagnetic effect results when the product of a grain's volume (V) and its anisotropy energy (Ku) fall below a certain value such that the magnetization of that grain may flip spontaneously due to thermal vibrations. Where this occurs, data stored on the disk is corrupted. Thus, while it is desirable to make smaller grains to support higher density recording with less noise, grain miniaturization is inherently limited by the superparamagnetic effect.
In response to this problem, engineers have developed patterned media, where the magnetic thin film layer is created as an ordered array of highly uniform islands, each island capable of storing an individual bit. Each bit may be one grain, or several exchange coupled grains, rather than a collection of random decoupled grains. In this manner, patterned media effectively reduces noise by imposing sharp magnetic transitions at well-defined pre-patterned positions.
Indeed, since patterned media allows data to be stored in pre-patterned islands containing a single grain or a small number of grains, rather than the much larger number of random grains required in conventional media, patterned media effectively circumvents the density limitations imposed by the superparamagnetic effect, extending by at least an order of magnitude the range of densities at which thermal stability is achieved. Despite the advantages of such media, however, cost-effective methods of mass producing patterned media have not been shown.
One method used to produce patterned media comprises the steps of: (1) creating a physical master pattern of features on a substrate; (2) replicating the features of the master pattern in a resist pattern on a disk substrate using nanoimprint lithography; (3) transferring the pattern into the disk substrate by etching; and (4) blanket depositing a magnetic and overcoat layer on the patterned disk substrate. Creation of the master pattern for densities in the range of 1 Terabit/square inch and beyond is difficult to achieve by conventional lithographic techniques such as optical or e-beam lithography because the features are too small to be compatible with either of these techniques. Thus, for hard disks to realize the potential densities that patterned media may provide, a master pattern generation process is needed to generate features in the required density range.
Although methods have been proposed for overcoming some of the density limitations of conventional lithographic manufacturing methods generally, such methods are not readily applicable to disk drive technology. For example, tight position tolerances resulting from track-following servo requirements as well as read and write channel clocking requirements limit the usefulness of proposed self-assembly processes, where molecules spontaneously organize into well-defined aggregates. Also, known lithographic processes for manufacturing disks are both time and labor intensive, making such processes costly and generally impractical for high volume media fabrication.
Accordingly, a need exists for a practical, attainable apparatus, system, and method for increasing storage density in patterned media. Beneficially, such an apparatus, system and method would increase media data storage capabilities, maintain precise data position control, and increase media data resolution while limiting expenses traditionally associated with patterned media fabrication. Such apparatuses, systems and methods are disclosed and claimed herein.